Data storage devices for various storage media, such as optical disks, magnetic tapes, and semiconductor memories, are known. Hard disk devices or hard disk drives (HDD) including magnetic disks are one type of the data storage devices.
The magnetic disks included in the HDD each have concentrically formed tracks, each of which is divided into sectors. Each sector stores data and address information of the sector. The magnetic disks are rotated at a speed as high as several thousand rotations per minute, and the access arm moves toward the center or outward based on the address information of the sector and a head provided at the tip of the access arm reads data (see FIG. 12). The data is read as signals, which are subjected to predetermined signal processing (such as waveform shaping and decoding processing) performed by a signal processing circuit and are then transmitted to a host. When write data or the like is transferred from the host, the signal processing circuit and so on process the data in a similarly manner and writes the processed data to the magnetic disks.
A SCSI (small computer system interface) protocol or ATA (advanced technology attachment) interface protocol is typically used as an interface protocol for the data transfer performed between the HDD and the host. In recent years, in an ATA interface in particular, serial ATA (SATA) has been proposed in which the conventionally used parallel transfer system is changed to the serial transfer system. The SATA allows high-speed transfer to be achieved with a simple cable structure.
However, in order to maintain serial communication with the host, the SATA system requires another power in addition to the power consumed in the conventional parallel transfer system. Thus, the SATA system is equipped with power saving functions for reducing the power consumption to the level that is substantially equal to that consumed in the parallel transfer system. As one of the power saving functions, device initiated SATA power management (DIPM) is available. The DIPM is aimed to reduce the power by reducing the level of the interface signal, which constantly consumes power, to a minimum level when no communication is performed.
A control method for the DIPM is that, when power saving is executed during a read seek operation, the HDD 1 wakes up (resumes) from the power saving state when data can be read from a target sector. The wake up time (the time for resuming from the power saving state) acts as an overhead, which delays the start of transfer of the data to the host. As a result, the performance of a read command for, particularly, a small sector size declines.
FIG. 13 illustrates an example of such a decline in the performance of a read command. Ratio INT (interrupt) illustrated in FIG. 13 indicates timing at which a preparation, such as a read seek operation, for reading data from a magnetic disk is completed and data transfer to the host can be started, and is associated with transfer rates between the host and the disk.
As illustrated in FIG. 13, the DIPM power saving is performed in the read seek operation, the ratio INT is reached at the timing at which data is readable from a target sector, and the HDD wakes up from the power saving state. Since the data transfer cannot be performed in the wake up time, a delay occurs correspondingly. In the known DIPM control method, the HDD wakes up from the power saving state at the ratio INT timing, as described above. Thus, there are problems in that the start of the data transfer is delayed and the performance declines.
As a technology for improving the performance of a HDD, native command queuing (NCQ) is available. The NCQ is a technology for improving the speed of accessing data. In the NCQ, instructions for the HDD (the instructions are one type of control commands issued from the host to the HDD) are stored in a queue and the instructions are rearranged so as to minimize the disk rotation and the head seek operation of the HDD.
A method for the NCQ control is that a data service for an NCQ command is unconditionally executed during the read seek operation and before the ratio INT timing. FIG. 14 illustrates an example of a decline in the performance of a read command based on NCQ.
In FIG. 14, during a read seek operation and before the ratio INT timing, data services 1 to 3 for NCQ commands are executed. Consequently, data is read from a target sector and the execution of the data services are continued even when the data can be transferred. Thus, the start of the transfer of the data for the read command to the host is delayed. Thus, the technology that is supposed to improve the performance of the HDD conversely provides a problem in that the performance of the HDD declines.
Japanese Laid-open Patent Publication No. 2006-139548, Japanese Laid-open Patent Publication No. 2006-139459, and Japanese Laid-open Patent Publication No. 2006-164012 disclose methods for reducing power consumption while preventing a decline in the performance of HDDs. More specifically, Japanese Laid-open Patent Publication No. 2006-139548 and Japanese Laid-open Patent Publication No. 2006-139459 propose methods for preventing a decline in the performance of the HDD by selecting a task that can be performed within a time when the bus is open, and Japanese Laid-open Patent Publication No. 2006-164012 proposes a power saving mode for preventing a decline in the performance of the HDD for host initiated SATA power management (HIPM).